1. Field of the Invention
The invention relates to processes for synthesis of bisphenols and more particularly to recovery of phenol from waste streams, the effluent of bisphenol synthesis.
2. Brief Description of Related Art
Bisphenols are commercially prepared by condensing 2 moles of phenol with a mole of ketone in the presence of an acid catalyst. The phenol is present in a molar excess of the stoichiometric requirement. During the condensation, a number of isomeric forms of the product bisphenol are formed which are contaminants of the desired bisphenol.
Among the by-product contaminant forms of phenol and bisphenol are, for example, o,p-isomers of bisphenol, chroman I and chroman II. These contaminants are carried in the product stream from the condensation reaction zone, with water, trace quantities of acidic materials derived from the catalyst, unreacted phenol and unreacted ketone. Currently, the purification of the desired product bisphenol is a costly and multi-step procedure.
There are two commercially important processes for the synthesis of bisphenols currently in use. The earlier process is called the "HCl" process, in reference to the acidic catalyst employed, hydrogen chloride [HCl]. Briefly, glass lined vessels are charged in a batch/continuous fashion, with phenol, ketone and recycled by-products from earlier synthesis. This mixture is continually kept under a positive pressure of hydrogen chloride gas which catalyzes the formation of bisphenol.
The second commercial synthesis reaction consists of passing phenol, ketone and the recycled by-products through a stationary bed of acidic ion exchange resin (IER) catalyst. This can be done in one of two ways; first, until essentially complete ketone depletion; second, and most desirable, is "partial ketone conversion". This technology is described in U.S. Pat. No. 5,315,042 which is hereby incorporated herein by reference thereto.
Representative of more detailed descriptions of the above commercial processes for condensing phenol with acetone to obtain bisphenol-A (sometimes referred to herein as BPA) are those found in the U.S. Pat. Nos. 4,346,247; 4,396,728; 4,400,555; 4,424,283; 4,584,416; 4,766,254 and 4,847,433; all of which are incorporated herein by reference thereto. The factor shared by all of these known methods and processes is the need to purify and recover the product bisphenol in steps subsequent to the condensation reaction. Another shared factor is described in the U.S. Pat. No. 4,327,229 (incorporated herein by reference thereto) which concerns the recovery of valuable products and by-products of bisphenol-A synthesis. In U.S. Pat. No. 4,327,229 recognition is given to a problem concerning the preparative reaction effluent, which contains unreacted phenol, unreacted acetone, acid residues of the catalyst, water, tars and by-product isomers of bisphenol-A in admixture with the desired bisphenol-A.
As mentioned above, all of the commercial processes to prepare bisphenol include costly multi-step purification procedures entailing distillations, crystallizations, solvent extractions, evaporations and like procedures. Where bisphenol is separated from the contaminants and purified by crystallization, a mother liquor is obtained which contains (after dewatering) lower boiling reaction by-products, bisphenol and higher boiling reaction by-products to name a few components. A part of this mother liquor is conventionally recycled to the condensation reactor for utilization in the preparative process, but a small part is purged from the process line to maintain the quality of the desired bisphenol and to avoid build-up of the undesirable by-products in the process line. The purged mother liquor may be subjected to further treatment to extract solvents, phenol, acetone, bisphenol, water and other useful components, but there ultimately results a residual tar which is generally burned as a means of disposal. However, as stated in the U.S. Pat. No. 4,327,229, "it has been calculated that substantial amounts of phenol and re-usable bisphenol-A values can be derived from the tars and liquors derived from the process of making bisphenol-A, and there still remains the need to treat the tars and residues resulting from the initial reaction of the phenol and acetone to recover all useful products in order to enhance the value of the bisphenol-A process."
The present invention is an improvement in the utilization of the tar residues of the commercial bisphenol process, using it as a feedstock to recover phenols. The process comprises cracking the tars to obtain phenols. A preferred embodiment of the present invention is an improvement in the utilization of the tar residues of the commercial acidic ion exchange resin catalyst bisphenol process wherein phenol, acetone and recycled by-product are passed through a stationary bed of the ion exchange resin which is used as a feedstock to recover phenols.
Prior to the present invention, it was known that phenols could be recovered from the above-described tar residues by thermal cracking in the presence of aluminum compounds and molecular sieve catalysts; see for example the descriptions set forth in the U.S. Pat. No. 4,277,628 (Carnahan) and U.S. Pat. No. 4,351,966 (Flock). However, these procedures can be relatively expensive for the amount of phenol recovered. We have now developed a homogeneous catalytic cracking process based on catalysis with aromatic sulfonic acids. The process of the present invention provides quantitative phenol recovery with high purity, low cost and easy handling.